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Leitch B. The Impact of Glutamatergic Synapse Dysfunction in the Corticothalamocortical Network on Absence Seizure Generation. Front Mol Neurosci 2022; 15:836255. [PMID: 35237129 PMCID: PMC8882758 DOI: 10.3389/fnmol.2022.836255] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2021] [Accepted: 01/18/2022] [Indexed: 12/02/2022] Open
Abstract
Childhood absence epilepsy (CAE) is the most common pediatric epilepsy affecting 10–18% of all children with epilepsy. It is genetic in origin and the result of dysfunction within the corticothalamocortical (CTC) circuitry. Network dysfunction may arise from multifactorial mechanisms in patients from different genetic backgrounds and thus account for the variability in patient response to currently available anti-epileptic drugs; 30% of children with absence seizures are pharmaco-resistant. This review considers the impact of deficits in AMPA receptor-mediated excitation of feed-forward inhibition (FFI) in the CTC, on absence seizure generation. AMPA receptors are glutamate activated ion channels and are responsible for most of the fast excitatory synaptic transmission throughout the CNS. In the stargazer mouse model of absence epilepsy, the genetic mutation is in stargazin, a transmembrane AMPA receptor trafficking protein (TARP). This leads to a defect in AMPA receptor insertion into synapses in parvalbumin-containing (PV+) inhibitory interneurons in the somatosensory cortex and thalamus. Mutation in the Gria4 gene, which encodes for the AMPA receptor subunit GluA4, the predominant AMPA receptor subunit in cortical and thalamic PV + interneurons, also leads to absence seizures. This review explores the impact of glutamatergic synapse dysfunction in the CTC network on absence seizure generation. It also discusses the cellular and molecular mechanisms involved in the pathogenesis of childhood absence epilepsy.
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Brown JW, Taheri A, Kenyon RV, Berger-Wolf TY, Llano DA. Signal Propagation via Open-Loop Intrathalamic Architectures: A Computational Model. eNeuro 2020; 7:ENEURO.0441-19.2020. [PMID: 32005750 PMCID: PMC7053175 DOI: 10.1523/eneuro.0441-19.2020] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2019] [Revised: 01/13/2020] [Accepted: 01/20/2020] [Indexed: 01/06/2023] Open
Abstract
Propagation of signals across the cerebral cortex is a core component of many cognitive processes and is generally thought to be mediated by direct intracortical connectivity. The thalamus, by contrast, is considered to be devoid of internal connections and organized as a collection of parallel inputs to the cortex. Here, we provide evidence that "open-loop" intrathalamic pathways involving the thalamic reticular nucleus (TRN) can support propagation of oscillatory activity across the cortex. Recent studies support the existence of open-loop thalamo-reticulo-thalamic (TC-TRN-TC) synaptic motifs in addition to traditional closed-loop architectures. We hypothesized that open-loop structural modules, when connected in series, might underlie thalamic and, therefore cortical, signal propagation. Using a supercomputing platform to simulate thousands of permutations of a thalamocortical network based on physiological data collected in mice, rats, ferrets, and cats and in which select synapses were allowed to vary both by class and individually, we evaluated the relative capacities of closed-loop and open-loop TC-TRN-TC synaptic configurations to support both propagation and oscillation. We observed that (1) signal propagation was best supported in networks possessing strong open-loop TC-TRN-TC connectivity; (2) intrareticular synapses were neither primary substrates of propagation nor oscillation; and (3) heterogeneous synaptic networks supported more robust propagation of oscillation than their homogeneous counterparts. These findings suggest that open-loop, heterogeneous intrathalamic architectures might complement direct intracortical connectivity to facilitate cortical signal propagation.
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Affiliation(s)
- Jeffrey W Brown
- College of Medicine, University of Illinois at Urbana-Champaign, Urbana, IL 61801
| | - Aynaz Taheri
- Department of Computer Science, University of Illinois at Chicago, Chicago, IL 60607
| | - Robert V Kenyon
- Department of Computer Science, University of Illinois at Chicago, Chicago, IL 60607
| | - Tanya Y Berger-Wolf
- Department of Computer Science, University of Illinois at Chicago, Chicago, IL 60607
| | - Daniel A Llano
- College of Medicine, University of Illinois at Urbana-Champaign, Urbana, IL 61801
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL 61801
- Neuroscience Program, University of Illinois at Urbana-Champaign, Urbana, IL 61801
- Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, IL 61801
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Broicher T, Seidenbecher T, Meuth P, Munsch T, Meuth SG, Kanyshkova T, Pape HC, Budde T. T-current related effects of antiepileptic drugs and a Ca2+ channel antagonist on thalamic relay and local circuit interneurons in a rat model of absence epilepsy. Neuropharmacology 2007; 53:431-46. [PMID: 17675191 DOI: 10.1016/j.neuropharm.2007.05.030] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2006] [Revised: 05/29/2007] [Accepted: 05/30/2007] [Indexed: 11/19/2022]
Abstract
Channel blocking, anti-oscillatory, and anti-epileptic effects of clinically used anti-absence substances (ethosuximide, valproate) and the T-type Ca2+ current (IT) blocker mibefradil were tested by analyzing membrane currents in acutely isolated local circuit interneurons and thalamocortical relay (TC) neurons, slow intrathalamic oscillations in brain slices, and spike and wave discharges (SWDs) occurring in vivo in Wistar Albino Glaxo rats from Rijswijk (WAG/Rij). Substance effects in vitro were compared between WAG/Rij and a non-epileptic control strain, the ACI rats. Ethosuximide (ETX) and valproate were found to block IT in acutely isolated thalamic neurons. Block of IT by therapeutically relevant ETX concentrations (0.25-0.75 mM) was stronger in WAG/Rij, although the maximal effect at saturating concentrations (>or=10 mM) was stronger in ACI. Ethosuximide delayed the onset of the low threshold Ca2+ spike (LTS) of neurons recorded in slice preparations. Mibefradil (>or=2 microM) completely blocked IT and the LTS, dampened evoked thalamic oscillations, and attenuated SWDs in vivo. Computational modeling demonstrated that the complete effect of ETX can be replicated by a sole reduction of IT. However, the necessary degree of IT reduction was not induced by therapeutically relevant ETX concentrations. A combined reduction of IT, the persistent sodium current, and the Ca2+ activated K+ current resulted in an LTS alteration resembling the experimental observations. In summary, these results support the hypothesis of IT reduction as part of the mechanism of action of anti-absence drugs and demonstrate the ability of a specific IT antagonist to attenuate rhythmic burst firing and SWDs.
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Affiliation(s)
- Tilman Broicher
- Institut für Physiologie I, Westfälische Wilhelms-Universität Münster, Robert-Koch-Str. 27a, D-48149 Münster, Germany
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Massimini M, Huber R, Ferrarelli F, Hill S, Tononi G. The sleep slow oscillation as a traveling wave. J Neurosci 2004; 24:6862-70. [PMID: 15295020 PMCID: PMC6729597 DOI: 10.1523/jneurosci.1318-04.2004] [Citation(s) in RCA: 748] [Impact Index Per Article: 37.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2004] [Revised: 06/03/2004] [Accepted: 06/17/2004] [Indexed: 11/21/2022] Open
Abstract
During much of sleep, virtually all cortical neurons undergo a slow oscillation (<1 Hz) in membrane potential, cycling from a hyperpolarized state of silence to a depolarized state of intense firing. This slow oscillation is the fundamental cellular phenomenon that organizes other sleep rhythms such as spindles and slow waves. Using high-density electroencephalogram recordings in humans, we show here that each cycle of the slow oscillation is a traveling wave. Each wave originates at a definite site and travels over the scalp at an estimated speed of 1.2-7.0 m/sec. Waves originate more frequently in prefrontal-orbitofrontal regions and propagate in an anteroposterior direction. Their rate of occurrence increases progressively reaching almost once per second as sleep deepens. The pattern of origin and propagation of sleep slow oscillations is reproducible across nights and subjects and provides a blueprint of cortical excitability and connectivity. The orderly propagation of correlated activity along connected pathways may play a role in spike timing-dependent synaptic plasticity during sleep.
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Affiliation(s)
- Marcello Massimini
- Department of Psychiatry, University of Wisconsin-Madison, Madison, Wisconsin 53719, USA
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Destexhe A, Sejnowski TJ. Interactions between membrane conductances underlying thalamocortical slow-wave oscillations. Physiol Rev 2003; 83:1401-53. [PMID: 14506309 PMCID: PMC2927823 DOI: 10.1152/physrev.00012.2003] [Citation(s) in RCA: 185] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Neurons of the central nervous system display a broad spectrum of intrinsic electrophysiological properties that are absent in the traditional "integrate-and-fire" model. A network of neurons with these properties interacting through synaptic receptors with many time scales can produce complex patterns of activity that cannot be intuitively predicted. Computational methods, tightly linked to experimental data, provide insights into the dynamics of neural networks. We review this approach for the case of bursting neurons of the thalamus, with a focus on thalamic and thalamocortical slow-wave oscillations. At the single-cell level, intrinsic bursting or oscillations can be explained by interactions between calcium- and voltage-dependent channels. At the network level, the genesis of oscillations, their initiation, propagation, termination, and large-scale synchrony can be explained by interactions between neurons with a variety of intrinsic cellular properties through different types of synaptic receptors. These interactions can be altered by neuromodulators, which can dramatically shift the large-scale behavior of the network, and can also be disrupted in many ways, resulting in pathological patterns of activity, such as seizures. We suggest a coherent framework that accounts for a large body of experimental data at the ion-channel, single-cell, and network levels. This framework suggests physiological roles for the highly synchronized oscillations of slow-wave sleep.
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Affiliation(s)
- A Destexhe
- Unité de Neurosciences Intégratives et Computation-nelles, Centre National de la Recherche Scientifique, Gif-sur-Yvette, France.
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Porcello DM, Smith SD, Huguenard JR. Actions of U-92032, a T-type Ca2+ channel antagonist, support a functional linkage between I(T) and slow intrathalamic rhythms. J Neurophysiol 2003; 89:177-85. [PMID: 12522170 DOI: 10.1152/jn.00667.2002] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Thalamic relay neurons express high levels of T-type Ca(2+) channels, which support the generation of robust burst discharges. This intrinsically mediated form of phasic spike firing is thought to be critical in the generation of slow (3-4 Hz) synchronous oscillatory activity of absence epilepsy. Recordings made from brain slices or whole animals have shown that slow synchronous absence-like activity can be abolished when Ca(2+)-dependent burst firing in relay neurons is interrupted by the pharmacological or genetic inactivation of T-channels. Because succinimide drugs act as incomplete and nonspecific antagonists, we tested whether the novel T-channel antagonist U-92032 could provide stronger support for a role of T-channels in slow oscillatory activity. Ca(2+)-dependent rebound (LTS) bursts were recorded using whole cell current clamp in relay cells of the ventral basal complex (VB) from thalamic slices of adult rats. We used LTS kinetics to measure the availability of T-channels in VB cells after TTX. U-92032 (1 and 10 microM) reduced the maximum rate of depolarization of the isolated LTS by 51% and 90%, respectively, compared with the 35% reduction due to 2 mM methylphenylsuccinimide (MPS), the active metabolite of the antiabsence drug methsuximide. U-92032 (1 and 10 microM) also suppressed evoked, slow oscillations in thalamic slices with a time course similar for observed intracellular effects. Unlike MPS, we observed no substantial effects of short-term U-92032 applications (< or =2 h) on the generation of action potentials in VB cells. Our findings show U-92032 is a more potent, effective, and specific T-channel antagonist than previously studied succinimide antiabsence drugs and that it dramatically reduces epileptiform synchronous activity. This suggests that U-92032 or other specific T-channel antagonists may provide effective drug treatments for absence epilepsy.
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Affiliation(s)
- Darrell M Porcello
- Department of Neurology and Neurological Sciences, Stanford University Medical Center, California 94305, USA
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Rubin J, Terman D, Chow C. Localized bumps of activity sustained by inhibition in a two-layer thalamic network. J Comput Neurosci 2001; 10:313-31. [PMID: 11443288 DOI: 10.1023/a:1011220332546] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Based on head direction experiments in rats, the existence of localized bumps of thalamic activity has been proposed. We computationally demonstrate the existence of a novel class of localized bump solutions in a two-layer conductance-based thalamic network and analyze the mechanisms behind these stable patterns. In contrast to previous models of bump activity, here inhibition plays a crucial role in initially spreading neuronal firing and in subsequently sustaining it. In our model, we incorporate local strong, fast GABA(A) inhibition and diffuse weak, slow GABA(B) inhibition, based on previous biophysical experiments. These forms of inhibition contribute in different, yet complementary, ways to the observed pattern formation.
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Affiliation(s)
- J Rubin
- The Ohio State University, Ohio, USA.
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Abstract
NEURON is a simulation environment for models of individual neurons and networks of neurons that are closely linked to experimental data. NEURON provides tools for conveniently constructing, exercising, and managing models, so that special expertise in numerical methods or programming is not required for its productive use. This article describes two tools that address the problem of how to achieve computational efficiency and accuracy.
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Affiliation(s)
- M L Hines
- Department of Computer Science, Yale University, New Haven Connecticut 06520-8001, USA. michael.hines@yale
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Reciprocal inhibitory connections produce desynchronizing phase lags during intrathalamic oscillations. Neurocomputing 2000. [DOI: 10.1016/s0925-2312(00)00206-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Abstract
Mice with an inactivated GABA(A) receptor beta(3) subunit gene have features of Angelman syndrome, including absence-like seizures. This suggests the occurrence of abnormal hypersynchrony in the thalamocortical system. Within the thalamus, the efficacy of inhibitory synapses between thalamic reticular (RE) neurons is selectively compromised, and thalamic oscillations in vitro are prolonged and lack spatial phase gradients (). Here we used computational models to examine how intra-RE inhibition regulates intrathalamic oscillations. A major effect is an abbreviation of network responses, which is caused by long-lasting intra-RE inhibition that shunts recurrent excitatory input. In addition, differential activation of RE cells desynchronizes network activity. Near the slice center, where many cells are initially activated, there is a resultant high level of intra-RE inhibition. This leads to RE cell burst truncation in the central region and a gradient in the timing of thalamocortical cell activity similar to that observed in vitro. Although RE cell burst durations were shortened by this mechanism, there was very little effect on the times at which RE cells began to burst. The above results depended on widespread stimuli that activated RE cells in regions larger than the diameter of intra-RE connections. By contrast, more focal stimuli could elicit oscillations that lasted several cycles and remained confined to a small region. These results suggest that intra-RE inhibition restricts intrathalamic activity to particular spatiotemporal patterns to allow focal recurrent activity that may be relevant for normal thalamocortical function while preventing widespread synchronization as occurs in seizures.
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